---
name: "PDL::GSL::DIFF"
section: "3pm"
platform: "linux"
package: "pdl"
version: "1:2.081-2"
release: "Debian 12 (Bookworm)"
platforms: ["linux"]
url: "https://new.carta.tech/PDL::GSL::DIFF"
---

# PDL::GSL::DIFF(3pm)

PDL interface to numerical differentiation routines in GSL

## NAME

PDL::GSL::DIFF - PDL interface to numerical differentiation routines in GSL

## DESCRIPTION

This is an interface to the numerical differentiation package present in the  GNU Scientific Library.

## SYNOPSIS

```
   use PDL;
   use PDL::GSL::DIFF;
   my $x0 = 3.3;
   my @res = gsldiff(\&myfunction,$x0);
   # same as above:
   @res = gsldiff(\&myfunction,$x0,{Method => 'central'});
   # use only values greater than $x0 to get the derivative
   @res =  gsldiff(\&myfunction,$x0,{Method => 'forward'});

   # use only values smaller than $x0 to get the derivative
   @res = gsldiff(\&myfunction,$x0,{Method => 'backward'});
   sub myfunction{
     my ($x) = @_;
     return $x**2;
   }
#line 61 "DIFF.pm"
```

## FUNCTIONS

### diff\_central

```
  Signature: (double x(); double [o] res(); double [o] abserr(); SV* function)
```

info not available

diff\_central does not process bad values. It will set the bad-value flag of all output ndarrays if the flag is set for any of the input ndarrays.

### diff\_backward

```
  Signature: (double x(); double [o] res(); double [o] abserr(); SV* function)
```

info not available

diff\_backward does not process bad values. It will set the bad-value flag of all output ndarrays if the flag is set for any of the input ndarrays.

### diff\_forward

```
  Signature: (double x(); double [o] res(); double [o] abserr(); SV* function)
```

info not available

diff\_forward does not process bad values. It will set the bad-value flag of all output ndarrays if the flag is set for any of the input ndarrays.

### gsldiff

This functions serves as an interface to the three differentiation  functions present in GSL: gsl\_diff\_central, gsl\_diff\_backward and  gsl\_diff\_forward. To compute the derivative, the central method uses  values greater and smaller than the point at which the derivative is  to be evaluated, while backward and forward use only values smaller  and greater respectively. **gsldiff()** returns both the derivative  and an absolute error estimate. The default  method is 'central',  others can be specified by passing an option.

Please check the GSL documentation for more information.

Usage:

```
  ($d,$abserr) = gsldiff($function_ref,$x,{Method => $method});
```

Example:

```
  #derivative using default method ('central')
  ($d,$abserr) = gsldiff(\&myf,3.3);
  #same as above with method set explicitly
  ($d,$abserr) = gsldiff(\&myf,3.3,{Method => 'central'});
  #using backward & forward methods
  ($d,$abserr) = gsldiff(\&myf,3.3,{Method => 'backward'});
  ($d,$abserr) = gsldiff(\&myf,3.3,{Method => 'forward'});
  sub myf{
    my ($x) = @_;
    return exp($x);
  }
```

## BUGS

Feedback is welcome. Log bugs in the PDL bug database (the database is always linked from \<http://pdl.perl.org\>).

## SEE ALSO

PDL

The GSL documentation is online at

```
  http://www.gnu.org/software/gsl/manual/
```

## AUTHOR

This file copyright (C) 2003 Andres Jordan \<andresj@physics.rutgers.edu\> All rights reserved. There is no warranty. You are allowed to redistribute  this software documentation under certain conditions. For details, see the file COPYING in the PDL distribution. If this file is separated from the PDL distribution, the copyright notice should be included in the file.

The GSL differentiation routines were written by David Morrison.